Обсуждение: syntax question

On Thu, Jun  3, 2021 at 08:58:03PM +0200, Marc Millas wrote:
> Hi,
> 
> within a function, I want to create another function.
> no pb.
> but if I write:
> declare bidule text;
> begin
> bidule:='myfunc';
> create function bidule() ...
> 
> 
> it does create a function named bidule and not myfunc.
> so I am obviously missing something too obvious.

You can't create functions inside of functions;  same for procedures.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.

On 6/3/21 12:01 PM, Bruce Momjian wrote:
> On Thu, Jun  3, 2021 at 08:58:03PM +0200, Marc Millas wrote:
>> Hi,
>>
>> within a function, I want to create another function.
>> no pb.
>> but if I write:
>> declare bidule text;
>> begin
>> bidule:='myfunc';
>> create function bidule() ...
>>
>>
>> it does create a function named bidule and not myfunc.
>> so I am obviously missing something too obvious.
> 
> You can't create functions inside of functions;  same for procedures.
> 

Sure you can:

CREATE OR REPLACE FUNCTION public.test_fnc()
  RETURNS void
  LANGUAGE plpgsql
AS $function$
DECLARE
      bidule text;
BEGIN
bidule:='myfunc';
EXECUTE  'create function ' ||  bidule || '() RETURNS void language 
plpgsql AS $fnc$ BEGIN END; $fnc$ ';
END;


$function$

select test_fnc();
  test_fnc
----------

  \df myfunc
                         List of functions
  Schema |  Name  | Result data type | Argument data types | Type
--------+--------+------------------+---------------------+------
  public | myfunc | void             |                     | func


Whether you should is another question.


-- 
Adrian Klaver
adrian.klaver@aklaver.com

Adrian Klaver <adrian.klaver@aklaver.com> writes:
> On 6/3/21 12:01 PM, Bruce Momjian wrote:
>> On Thu, Jun  3, 2021 at 08:58:03PM +0200, Marc Millas wrote:
>>> within a function, I want to create another function.

>> You can't create functions inside of functions;  same for procedures.

> Sure you can:

Yeah.  The actual problem here is that Marc is expecting variable
substitution to occur within a utility (DDL) statement, which it
doesn't.  The workaround is to build the command as a string and
use EXECUTE, as Adrian illustrated:

> EXECUTE  'create function ' ||  bidule || '() RETURNS void language
> plpgsql AS $fnc$ BEGIN END; $fnc$ ';

This is not terribly well explained in the existing docs.  I tried
to improve the explanation awhile ago in HEAD:

https://www.postgresql.org/docs/devel/plpgsql-statements.html#PLPGSQL-STATEMENTS-GENERAL-SQL

            regards, tom lane

On Thu, Jun  3, 2021 at 03:21:15PM -0400, Tom Lane wrote:
> Adrian Klaver <adrian.klaver@aklaver.com> writes:
> > On 6/3/21 12:01 PM, Bruce Momjian wrote:
> >> On Thu, Jun  3, 2021 at 08:58:03PM +0200, Marc Millas wrote:
> >>> within a function, I want to create another function.
> 
> >> You can't create functions inside of functions;  same for procedures.
> 
> > Sure you can:
> 
> Yeah.  The actual problem here is that Marc is expecting variable
> substitution to occur within a utility (DDL) statement, which it
> doesn't.  The workaround is to build the command as a string and
> use EXECUTE, as Adrian illustrated:
> 
> > EXECUTE  'create function ' ||  bidule || '() RETURNS void language 
> > plpgsql AS $fnc$ BEGIN END; $fnc$ ';
> 
> This is not terribly well explained in the existing docs.  I tried
> to improve the explanation awhile ago in HEAD:
> 
> https://www.postgresql.org/docs/devel/plpgsql-statements.html#PLPGSQL-STATEMENTS-GENERAL-SQL

Oh, I thought he wanted to declare a function inside the function that
could be called only by that function, like private functions in Oracle
packages can do.  Yes, you can create a function that defines a function
that can be called later.  I guess you could also create a function that
_conditionally_ creates a function that it can call itself too.  My
point is that you can't create a function that has function scope ---
they all have schema scope.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.

On 6/3/21 1:01 PM, Marc Millas wrote:
> thanks Adrian, exactly what I was missing :-)
> 
> about knowing if I should...
> We have to create a set of triggers (insert, update, delete) within a 
> huge set of tables. and that list of tables, and structure of them  can 
> be customized, maintained, ...
> so we were looking for a standard script to automatize the building of 
> the whole thing, taking list of columns  and constraints (for PK) 
> directly from pg_catalog.
> Now it works :-)
> 
> but.. why do you ask that question ? is there any king of hidden wolf we 
> didnt see ?

See David Johnston's answer. Nested quoting will drive you to drink(or 
drink more):)


> 
> 
> Marc MILLAS
> Senior Architect
> +33607850334
> www.mokadb.com <http://www.mokadb.com>
> 
> 
> 
> On Thu, Jun 3, 2021 at 9:11 PM Adrian Klaver <adrian.klaver@aklaver.com 
> <mailto:adrian.klaver@aklaver.com>> wrote:
> 
>     On 6/3/21 12:01 PM, Bruce Momjian wrote:
>      > On Thu, Jun  3, 2021 at 08:58:03PM +0200, Marc Millas wrote:
>      >> Hi,
>      >>
>      >> within a function, I want to create another function.
>      >> no pb.
>      >> but if I write:
>      >> declare bidule text;
>      >> begin
>      >> bidule:='myfunc';
>      >> create function bidule() ...
>      >>
>      >>
>      >> it does create a function named bidule and not myfunc.
>      >> so I am obviously missing something too obvious.
>      >
>      > You can't create functions inside of functions;  same for procedures.
>      >
> 
>     Sure you can:
> 
>     CREATE OR REPLACE FUNCTION public.test_fnc()
>        RETURNS void
>        LANGUAGE plpgsql
>     AS $function$
>     DECLARE
>            bidule text;
>     BEGIN
>     bidule:='myfunc';
>     EXECUTE  'create function ' ||  bidule || '() RETURNS void language
>     plpgsql AS $fnc$ BEGIN END; $fnc$ ';
>     END;
> 
> 
>     $function$
> 
>     select test_fnc();
>        test_fnc
>     ----------
> 
>        \df myfunc
>                               List of functions
>        Schema |  Name  | Result data type | Argument data types | Type
>     --------+--------+------------------+---------------------+------
>        public | myfunc | void             |                     | func
> 
> 
>     Whether you should is another question.
> 
> 
>     -- 
>     Adrian Klaver
>     adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com

bruce@momjian.us wrote:

Oh, I thought he wanted to declare a function inside the function that could be called only by that function, like private functions in Oracle packages can do.  Yes, you can create a function that defines a function that can be called later.  I guess you could also create a function that _conditionally_ creates a function that it can call itself too.  My point is that you can't create a function that has function scope — they all have schema scope.